Fusible and readily removable protective coating for metal articles, comprising ethyl cellulose and mineral oil



Patented Jan. 4, 1949 FUSIBLE AND READILY REMOVABLE PRO- TECTIVE COATING FORMETAL ARTICLES, COMPRISING ETI-IYL CELLULOSE AND MINERAL OIL Arthur E. Young, Midland, Mich,- assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Application August 27, 1945, Serial No. 613,015

This invention relates to fusible protective coating compositions of particular use in the protection during shipment and storage of metallic articles The compositions concerned are of the type which may be removed readily from coated articles prior to their use. This application discloses and claims compositions which are an improvement over the compositions disclosed and claimed for the same purpose in my copending application, Serial No. 551,075, filed August 24, 1944.

During the past few years, considerable attention has been devoted to the longstanding problem of protecting metallic and other rigid and semi-rigid articles during shipment and storage, without the necessity for packing such articles in grease or in prefabricated airtight containers. The problem has been especially acute with respect to the shipment and storage of machine parts, ordnance items, aircraft engine accessories, and other metallic articles for use in hot humid climates, where protection is required against rust and corrosion due to humidity and salt spray, as well as against the usual dirt and abrasion incident to shipment and bulk storage.

In my aforesaid copending application Serial No. 551,075 it is proposed to'coat the article requiring protection, by immersion in a molten bath of the claimed coating composition, removing the so-coated article from the bath to congeal the coating, and, when the article is to be used, stripping the coating from the article. The composition there claimed includes from 15 to 45 per cent of ethyl cellulose, from 25 to 75 per cent of mineral oil, and up to 45 per cent of a resin, up to 20 per cent of a plasticizer, and up to 1 per cent of an anti-skinning agent or antioxidant. The said application describes at length the manner in which the ingredientsmay be selected and combined, the conditions under which they may be fused, and the mode of application whereby they may be used to coat metal objects. The compositions of theprior application are superior to any previously available means for protecting metallic articles against the stated hazards,.and

6 Claims. (Cl. 260-47) 2 one end of the article in the melt, allow the coating tlnreon to cool, and then to dip the other end so that the last applied coating overlaps that previously .applied. The compositions of the aforesaid prior application are found not to have consistently a. perfect bond at the overlap. There is also room for improvement in the flexibility of the strippable melt coatings, so that they may be stripped in large pieces, even from very complex surfaces.

It is accordingly among the objects of the present invention to provide a composition which may be applied from the molten condition to articles requiring protection, and which will form a perfect seal along lines of overlap betweensuc- .cessively deposited portions of the coating. It is a further object to provide such a composition which has, as well, a sumcient degree of flexibility to be strippable in large pieces from the coated article prior to use. A related object is to provide a composition as aforesaid which represents a substantial improvement in bond and flexibility over strippable melt coatings heretofore known. Other and related objects may appear hereinafter.

The foregoing and related objects may be attained through the preparation and use, for the stated purpose, of a fusible composition, the

' essential ingredients of which are from 15 to they have become widely used by contractors to the military forces for the protection of items for overseas shipment. Experience has shown, however, that those prior compositions are somewhat defective in two of the desired attributes of such coatings. It is desired to improve the flexibility and the bond of the prior compositions.

In coating cost articles with thestripping type of melt coatings it is common practice to dip per cent of ethyl cellulose, from 35 to per centof mineral oil, from 7 to 30 per cent of a liquid styrene condensate having a molecular weight from 300 to 600, and from 3 to 12 per cent of a hydroxylated fatty oil. The specifications of the individual ingredients and the meaning of contain, as optional ingredients, from 0 to 10 per cent of a soft plasticizer, preferably one which is predominantly hydrocarbon in character, from 0 to 5 per cent of paraffin wax, and from 0 to 15 per cent of a solid coumarone-indene resin or, alternatively, from 0. to 5 per cent of a thermoplastic resinous terpene polymer.

Within the above-stated broad operative range of proportions of ingredients of the new compositions, a narrower range is found which gives consistently good results when tested against the re-' quirements of Ordnance Specification AXS-116'7, revision 2. These preferred compositions contain from 20 to 25 per cent of the stated type offethyl cellulose, from 40 to 50 per cent of the mineral oil, from 10 to 20 per cent of a liquid styrene condensate having a molecular weight between 300 and 400, and from 3 to 12 per cent of a hydroxylated fatty oil. As optional components, the previously suggested amounts of plasticizers, coumarone-indene resins, waxes, and the like, may be added, if desired. Any mineral wax present is preferably held to the range of 1 to 3 per cent. When the ingredients of the new composition are chosen in the manner outlined below, the compositions may be fused to form uniform melts which can be used to deposit coatings, with well bonded overlapping layers, on metal objects, and later can be stripped in large pieces from the coated article.

The ethyl cellulose employed in the new compositions must be one which is soluble in organic solvents. It should have an ethoxy content between 47 and 52 per cent, (preferably between 47.5 and 49.5 per cent), and should be of a medium-low viscosity type, i. e., one whose 5 per cent solution in 80:20 toluene-ethanol mixture has a viscosity of from 20 to 100 centipoises.

The mineral oil employed in the new and improved compositions should be one having a Saybolt viscosity of from 200 to 800 at 100 F., and an aniline point less than 90 C. These values may be determined by the methods described in ASTM D88-38 and D611-42T, respectively. All

of the mineral oils specifically named herein meet -the above-stated requirements, as do many other mineral oils.

The third and new ingredient of the compositions has been referred to above as a liquid styrene condensate." That term is used here in the same manner as it is used in a concurrently filed application of E. L, Kropscott et al., Serial No. 613,014, entitled Cellulose derivative compositions," to define a, liquid product having a molecular weight between about 300 and about 600 and being substantially identical with the product obtained by causing monomeric styrene or one of its simple homologs to react with itself or with other liquid monocycylic aromatic hydrocarbons in the presence of a condensation catalyst. It is known that styrene (and such homologs thereof as alpha-methyl styrene, or ortho-, metaand para-methyl styrene) can be caused to react with itself or with such aromatic hydrocarbons as toluene or xylene or other monocyclic hydrocarbons, at moderate temperatures between 50 C. and 150 C., in the presence of such condensation catalysts as 70-80 per cent sulfuric acid, or phosphoric acid, or antimony chloride, or acid activated bleaching earths, to give products which range from the simplest condensates and dimers, having molecular weights near 200, through increasingly complex liquid products, to brittle resins. It is upon the use of the simple liquid condensates and polymers, having molecular weights ranging from about 300 to about 600, preferably from 300 to about 400, that the present invention is based. For brevity, such liquid condensates and polymers, whether made from styrene itself or from its simple homologs, will be referred to in the following description as liquid styrene condensates.

The ethyl cellulose, mineral oil and liquid styrene condensate form the principal structural part of the herein described composition. Combinations of these three ingredients without further modifying agents are found to afford adequate protection to metal parts but they are too brittle to be used successfully as stripping compositions. The fourth essential ingredient, which is added to provide suppleness to the coating composition, is a hydroxylated fatty oil. The hydroxylated fatty oils include castor oil and the 4 blown vegetable oils, as well as liquid non-setting alkyd resin-modified castor oil. The latter may be prepared by heating together castor oil, glycerol and a dibasic acid such as succinic acid or sebacic acid. The alkyd resin-modified castor oils are available commercially under such trade names as Beckosoi 24 (manufactured by Reichhold Chemicals, Incorporated) and Paraplex RG-8 (manufactured by Resinous Products and Chemical Company).

The optional ingredients which may be added to provide specific eflects include such softening agents as diamyl naphthalene, petroleum waxes of naphthenic character, such as Gulf impregnating wax M, and the softer variety of conmarone-indene resins including, for example, a dibutyi phthalate-modifled coumarone-indene resin known commercially as Nevtex, manufactured by the Neville Company. There may also be added to the composition small amounts, not exceeding 5 per cent, of paraflln wax which may assist in reducing the moisture vapor transmission of the coating composition. In some few cases, it has been found desirable to add a small amount, up to 15 per cent, of a coumarone-indene resin having a melting point above 100 F. Alternative resinous ingredients which, however, can not be used satisfactorily in quantities greater than about 5 per cent, are thermoplastic terpene resins.

In combining the'various ingredients and in selecting the particular quantities of each to be employed, the requirements of Ordnance Specification AXS-1167, revision 2 must be kept in mind. The said specification relates to ethyl cellulose protective stripping compounds and establishes minimum values for tensile strength, elongation, and plasticity of coatings deposited from the composition, as well as maximum thickness of coating which may be deposited when a standard steel panel is dipped into the composition under specified conditions, and then removed. Thus, Specification AXE-1167, revision 2, requires that these compositions have a tensile strength greater than 450 pounds per square inch 1. e., greater than 32 kilograms per square centimeter. When the composition is first melted it should deposit coatings having elongation values greater than per cent and after having been heated for 48 hours at 375 F. the elongation of deposited coatings should be at least 50 per cent. The plasticity of the coating as determined on a Williams plastometer at 160 F. (using a 5 kilogram weight on a one-half inch pellet) should be greater than 150 mils. When a steel panel one-eighth inch thick is immersed in the molten composition for 5 minutes at 375 F. and removed, the coating adhering to the panel should be less than mils thick.

The following examples illustrate the practice of the invention:

Example I 24 parts by weight of ethyl cellulose having an ethoxy content of 48.5 per cent, and being of a type whose 5 per cent solution in 80:20 toluene-ethanol mixture has a viscosity of 50 centipoises, was dissolved by stirring in a heated mixture of 1 part of paraflln wax having a melting point of F., 10 parts of a liquid styrene Example II v A composition was prepared containing 22 parts of the same ethyl cellulose, 47 parts of the oil employed in Example I, 1 part of paramn wax, parts of liquid styrene condensate having a molecular weight of about 350, 10 parts of Paraplex RG-B and 10 parts of a coumarone-indene resin melting above100 F. Under the standard test conditions, this molten composition deposited coatings '19 mils thick, which coating had a plasticity of 165, an initial tensile strength of 35 kilograms per square centimeter, an initial elongation of. 95 per cent, a tensile strength, after 48 hours at 375 F., of 32 kilograms .per square centimeter and an elongation value after that period of 68 per cent. Coatings deposited after 48 to 64 hours of heating were '71 mils thick. This was highly flexible coating, which gave an excellent bond at the areas of overlap and which could be stripped in large pieces from the protected metal article, even when that article was highly irregular in shape.

Example III A composition was prepared identical with that in Example II except that a heat bodied castor oil was substituted for the Paraplex RG-8. This composition initially deposited coatings 81 mils thick and after 48 hours at 375 F. deposited coatings '72 mils thick. The tensile strength was 39 kilograms per square centimeter and the elongation value varied from 85 to 81 per cent. The plasticity was 158 mils.

Example IV Example V I The composition of Example II was varied by increasing the quantity of ethyl cellulose to 24 per cent and reducing the quantity of mineral oil (Gulf oil No. 565) to 45 per cent. This composition deposited coatings from freshly molten material 84 mils thick and, from material which had been heated for 48 hours at 375 F., about 74 mils thick. The initial tensile strength was 35 kilograms per square centimeter and that after 48 hours heating was 34 kilograms per square centimeter. The initial elongation value was 100 per cent, and the final value, '79 per cent. These coatings had a plasticity value of 164 mils. This was a very flexible composition which afforded excellent protection to complex metal parts and which could be readily stripped from such parts prior to their use, peeling off in large strips.

The examples have illustrated compositions containing from 22 to 24 per cent of ethyl cellulose, -from 44 to 47 per cent of mineral oil, 10 per cent of liquid styrene condensate, 10 per cent of hydroxylated vegetable oil, 1 to 2'per cent of parafllnwax, and 0 to 10 per cent of other ingredients. The invention is by no means limited to to per cent of a mineral oil having 9. Say- 6 compositions in this narrow range. as useful compositions for the intended purpose are obtained in the previously defined ranges of broader proportions.

The herein-described compositions are free from volatile solvents, and their use with solvents is not contemplated. They are fusible to form completely homogeneous melts which, when cooled to below 100 F. in contact with metal surfaces, form homogeneous, flexible, and easily removable coatings thereon, a substantially free from oily exudation.

I claim:

1. A fusible coating composition, free from volatile solvents,'.which is homogeneous in the molten state, and which congeals,- when cooled to below 100 F. in contact with a metal surface, to form thereon a homogeneous, supple, and easily removable coating, substantially free from oily exudation, comprising as principal constituents:

from 15 to 30 per cent of ethyl cellulose having an ethoxy content between 47 and 52 per cent; from bolt viscosity between 200 and 800 at 100 F., and an aniline point less than 90 C.; from 7 to 30 per cent of a liquid condensate having a molecular weight between 300 and 600 obtained by heating a material selected from the group consisting of (1) styrene, (2) the mono-methyl homologs of styrene, and (3) mixtures of the foregoing with a liquid monocyclic aromatic hydrocarbon from the group consisting of toluene and xylene, at a temperature between 50 and 150 C. in the presence of a condensation catalyst; and from 3 to 12 per cent of a hydroxylated fatty oil.

2. A fusible coating composition, free from volatile solvents, which is homogeneous in the molten state, and which congeals, when cooled to below 100 F. in contact with a metal surface, to form thereon a homogeneous, supple, and easily removable coating, substantially free from oily exudation, comprising as principal constituents: from 15 to 30 per cent of ethyl cellulose having an ethoxy content between 47.5 and 49.5 per cent; from 35 to 55 per cent of a mineral oil having a Saybolt viscosity between 200 and 800 at 100 F., and an aniline point less than 90 C.; from '7 to 30 per cent of a liquid condensate having a molecular weight between 300 and 400 obtained by heating a material selected from the group consisting of (1) styrene, (2) the monomethyl homologs of styrene, and (3) mixtures of. the foregoing with a liquid monocyclic aromatic hydrocarbon from the group consisting of toluene and xylene, at a temperature between 50 and 150 C. in the presence of a condensation catalyst; and from 3 to 12 per cent of a hydroxylated fatty oil.

3. A fusible coating composition, free from volatile solvents, which is homogeneous in the molten state, and which congeals, when cooled to below 100 F. in contact with a metal surface, to form thereon a homogeneous, supple, and easily removable coating, substantially free from oily exudation, comprising as principal constituents: from 20 to 25 per cent of ethyl cellulose having an ethoxy content of from 47.5 to 49.5 per cent, whose viscosity in a 5 per cent solution in :20 toluene-ethanol is from 20 to 100 centipoises; from 40 to 50 per cent of a mineral oil having a Saybolt viscosity between 200 and 800 at 100 F. and an aniline point less than C.; from 10 to 20 per cent of a liquid condensate having a molecular weight between 300 and 400 obtained consisting of (l) styrene, (2) the mono-methyl homologs of styrene, and (3) mixtures of the foregoing with a liquid monocyclic aromatic hydrocarbon from the group consisting of toluene and xylene, at a temperature between 50 and 150 C. in thepresence of a condensation catalyst; and from 3 to 12 per cent of a hydroxylated fatty oil.

4. A fusible coating composition, free from volatile solvents, which is homogeneous in the molten state, and which congeals, when cooled to below 100 F. in contact with a metal surface, to form thereon a homogeneous, supple, and easily removable coating, substantially free from oily exudation, comprising as principal constituents: from to per cent of ethyl cellulose having an ethoxy content of from 47.5 to 49.5 per cent, whose viscosity in a 5 per cent solution in 80:20 toluene-ethanol is from 20 to 100 centipoises;

from to per cent of a mineral oil having 20 a Saybolt viscosity between 200 and 800 at F. and an aniline point less than 90 C.; from 10 to 20 per cent of a liquid condensate having a molecular weight between 300 and 400 obtained by heating a material selected from the group 25 consisting'of (1) styrene, (2) the mono-methyl homologs of styrene, and (3) mixtures of the 8 foregoing with a liquid monocyclic aromatic hydrocarbon from the group consisting of toluene and xylene, at a temperature between 50 and C. in the presence of a condensation catalyst; from 3 to 12 per cent of a hydroxylated fatty oil; and from 1 to 3 per cent of paraffin wax.

5. fIhe composition as claimed in claim 1, wherein the hydroxylated fatty oil is castor oil. 6. Tlie composition as claimed in claim 1, wherein the hydroxylated fatty oil is a. liquid, non-setting, alkyd resin-modified castor oil.

ARTHUR E. YOUNG.

. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,249,280 Koch July 15, 1941 2,409,986 Salo Oct. 22, 1946 2,421,046 Warner et al May 27, 1947 FOREIGN PATENTS Number Country Date 397,554 Great Britain Aug. 28, 1933 

